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Use FFmpeg’s concat demuxer to play prerecorded files one after another into a single YouTube Live stream. It sets the order of the media and the timing relative to the stream—not calendar start times or a wall-clock schedule. To change blocks at a particular time, you need a separate scheduling process. The method also depends on compatible input files and does not guarantee that FFmpeg will run indefinitely or recover from failures.
What a concat file does—and what it does not do
An FFmpeg concat file is a plain-text list of media files. The concat demuxer reads the list in order and adjusts timestamps so each file follows the previous one. That makes it useful for feeding a sequence of prerecorded blocks through one FFmpeg output to YouTube Live.
The sequence is stream-relative: the next file starts after the preceding file according to its duration and timestamps. The list does not say “start this documentary at 8 p.m.” or otherwise schedule changes against the clock. YouTube broadcast events are a separate concern from the media sequence being sent by the encoder.
Check whether the files are suitable for the concat demuxer
Before writing the list, inspect the inputs. FFmpeg’s concat demuxer documentation says: “All files must have the same streams (same codecs, same time base, etc.).” In practice, confirm that the files have matching stream layouts and compatible codecs and time bases. Different lengths among streams within a file can also leave gaps.
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- Good candidate: the blocks were prepared with matching stream layouts, codecs, and time bases, and their duration metadata is accurate.
- Likely to need another approach: files have mismatched codecs, stream layouts, or time bases, or you need FFmpeg to reconcile differently encoded sources. FFmpeg’s FAQ recommends the concat filter when re-encoding is needed.
- Potential timing issue: a file reports an inaccurate duration. The demuxer uses a file’s duration to position the next one, so incorrect metadata can cause timestamp artifacts or misplaced transitions.
Do not assume that any collection of MP4 files can be joined cleanly with stream copy. The demuxer has compatibility requirements; when inputs do not meet them, use a workflow that re-encodes, such as the concat filter.
Create the FFmpeg concat file
- Put the blocks in playback order. Keep the concat text file and media paths organized so you can identify which block plays next.
- Create a plain-text file, for example
blocks.ffconcat, with onefiledirective per block:ffconcat version 1.0 file 'block-01.mp4' file 'block-02.mp4' file 'block-03.mp4' - Make the signature the exact first line if you want FFmpeg to recognize the format automatically. It must read
ffconcat version 1.0, with no extra spaces and no byte-order mark before it. - Use valid paths. The example assumes the files are accessible from the working directory. For other locations, use paths that resolve from where you run FFmpeg and follow FFmpeg’s concat syntax for escaping spaces and special characters. Test paths with unusual characters before relying on the list for a live run.
- Check durations before adding overrides. Usually, omit
durationdirectives when the file metadata is correct. Add adurationdirective when a reported duration is unavailable or inaccurate, and verify the intended cut point against the actual media: FFmpeg uses that value to position the next file. The directive changes sequence timing; it does not create a wall-clock schedule.
Send the sequence to YouTube Live with FFmpeg
- Get the ingest details in YouTube Studio. Create or select the broadcast and use the stream URL and stream key provided for its encoder setup. Treat the key as a password: do not publish it in an article, command history shared with others, screenshot, or public repository.
- Run FFmpeg with the concat file as input. This example re-encodes video and audio for the output rather than assuming that stream copy is suitable for every source:
ffmpeg -re -f concat -safe 0 -i blocks.ffconcat -c:v libx264 -c:a aac -f flv "rtmp://a.rtmp.youtube.com/live2/YOUR_STREAM_KEY"YOUR_STREAM_KEYis a placeholder, not a real key. Replace it locally with the stream key from YouTube Studio, and keep the command private. The example uses the standard YouTube RTMP ingest address; use the stream URL shown for your broadcast if YouTube Studio provides a different one. - Review the YouTube Live Control Room preview. Confirm that video and audio are arriving as intended, then use YouTube’s Go live action when appropriate. Starting the encoder transports media; it is not the same as managing or publishing the broadcast event.
- Monitor the run. Watch for FFmpeg errors, stalled output, or a block transition that differs from the intended sequence. A concat file defines media order; it is not a process supervisor and does not provide automatic recovery from a network or encoder failure.
The command is a starting point, not a universal YouTube encoding profile. Choose output settings that match the source material, available encoding capacity, and the requirements shown in YouTube Studio. The concat demuxer’s compatibility rules still apply even when the output is re-encoded.
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Keep media order separate from broadcast scheduling
YouTube models a broadcast event separately from the live stream resource used to transport encoder media. In its API documentation, YouTube describes a 24/7 broadcast continuing while another broadcast is started for an interview, with the feed continuing after that interview event is completed. This illustrates why changing or managing broadcast events is not the same operation as changing the ordered files in an FFmpeg concat input.
If you need a block to begin at a specific local time, or want a recurring day-by-day lineup, build or use a separate scheduler that controls the media sequence or broadcast operation. The concat file alone has no calendar awareness. Likewise, unattended monitoring, restarting a failed FFmpeg process, and network recovery require separate operational arrangements; the concat demuxer does not promise them.
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Plan archive expectations separately
YouTube Help says streams under 12 hours are automatically archived. That statement does not establish that one uninterrupted stream longer than 12 hours—such as a continuous 24/7 feed—will be archived as a single replay. If keeping a replay matters, design an explicit recording or archive workflow rather than relying on the concat list or assuming that a continuous broadcast produces one complete video.
Troubleshoot common problems
- FFmpeg does not auto-detect the concat format: confirm that
ffconcat version 1.0is the exact first line, without leading spaces or a byte-order mark. Keep-f concatin the command. - A file cannot be opened: check the path relative to the directory where FFmpeg is running, filename spelling, permissions, and escaping for spaces or special characters.
- Timestamp artifacts or a bad transition: compare the files’ actual durations with their metadata. Incorrect duration information can affect the timestamps assigned to following files; use a verified
durationoverride only when needed. - Gaps appear between blocks: check whether streams inside the inputs have matching lengths and whether each file’s stream layout and time base are compatible.
- The inputs fail to concatenate cleanly: inspect codecs, stream layouts, and time bases. If the files are incompatible, do not assume
-c copywill fix them; use a re-encoding workflow such as FFmpeg’s concat filter. - YouTube does not show the expected live preview: verify that FFmpeg is still running, the stream URL and key match the selected broadcast, and the encoder output is reaching the Live Control Room. Keep the key private while checking it.
- The stream stops after an error or disconnect: a concat script does not restart the process or restore a failed connection. Arrange separate monitoring and recovery if the operation must continue unattended.
Or let it run in the cloud
If your goal is to keep prerecorded blocks playing on a YouTube channel without leaving a computer running at home, StreamNeo is a cloud option. Upload a recording or build a playlist, add your YouTube stream key once, and go live; StreamNeo loops the uploaded video or playlist from the cloud. It does not stream from a camera or to other platforms.
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